Question

Guys help me to do this​

Answer 1

d= 29/3 - 10

d= -1/3

So,

Sn= 155=n/2 (20+(n-1) -1/3)

( by taking 3 as LCM on r.h.s)

310=n( 60- n+1)/3

930= 60n -n²+n

n²-61n+930=0

n²-31n-30n+930=0

n(n-31) -30 (n-31)=0

So, n= 31 or n= 30

Hope this helps. ^_^